(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to form a barrier layer on the surface of an opening in a low dielectric constant material, wherein the opening is to be used to accommodate a damascene type metal structure.
(2) Description of Prior Art
The use of copper interconnect structures, and of low constant dielectric (low k), layers, has allowed increased performance of semiconductor devices to be realized. Resistance decreases resulting from copper interconnect and via structures exhibiting lower sheet resistance than counterpart structures formed from aluminum based materials, in addition to the capacitance reductions obtained via the use of intermetal dielectric (IMD), layers comprised of low k layers such as fluorinated silicon glass (FSG), as well as other silicon low k (SiLK), materials, has allowed the reduction in resistance-capacitance (RC), to be achieved. However when forming a copper structure in an opening defined in a low k layer, barrier layers have to be used between the copper structure and the low k layer surface to avoid copper penetration into the low k, IMD material. Barrier layers such as titanium nitride have been used for this purpose. To perform the function of a thin barrier layer the material chosen should present excellent barrier properties in addition to being able to be formed using a deposition mode which will result in excellent barrier layer thickness uniformity on all surface of the opening in the low k layer.
Prior art, such as Lopatin et al, in U.S. Pat. No. 6,368,954 B1, Kwon et al, in U.S. Pat. No. 6,333,260 B1, and Kang et al, in U.S. Pat. No. 6,287,965 B1, describe barrier layers obtained via atomic layer deposition (ALD), procedures which satisfy the uniform deposition requirement. However the use of ALD procedures include precursor sequences using such materials as TiCl4 and NH3 which can penetrate porous regions of the exposed low k material resulting in undesired pinhole formation in the low k IMD layer. This invention will describe a novel barrier layer obtained via a two step deposition procedure which allows a thin uniform barrier layer to be deposited on the exposed surfaces of the opening in the low k layer, however without damage to the porous low k material.